Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Unlikely
- Size
- 2–2.5
Last week's snowfall has settled into soft slabs ranging from 1 to 3 feet thick. The problem is larger and more common at higher elevation, wind-drifted terrain on the north half of the compass. Although many of these slabs are bonding well now, instabilities may persist where they formed over a sporadic distribution of facets, surface hoar, or collapsible crusts on colder aspects. Evaluate slab size, weak layer characteristics, and terrain consequences before riding on slopes steeper than 35 degrees.
There is also isolated potential for larger and harder slab avalanches to break on weak layers in the middle or bottom of the snowpack from early and mid-winter dry spells. These avalanches are most likely to be triggered on the northern half of the compass and where the snowpack is unusually thin and weak. Be cautious of very steep, rocky, or wind-affected terrain with variable snow depths.
This persistent slab avalanche caught and carried a snowmobiler last weekend on East Beckwith. The avalanche broke on the January drought layer 2 to 3 feet deep in the middle of the snowpack. Note how the terrain has variable depths and shallow areas due to wind effects. (3/8/2025) Photo: Care Flight